EP0489318B1 - Mass and suspension polymers based on methyl methacrylate - Google Patents

Description

• a) 80 bis 100 Gew.-% Methylmethacrylat und
• b) 0 bis 20 Gew.-% weiteren radikalisch polymerisierbaren Monomeren,

erhältlich durch Polymerisation bei einer über den Großteil der Polymerisationszeit annähernd konstanten Temperatur zwischen 100 und 140°C mittels eines Initiatorsystems aus mindestens zwei peroxidischen Initiatoren I unterschiedlicher Zerfallstemperaturen T, bei denen jeweils die Hälfte des Initiators nach 1 h zerfallen ist, wobei

• der Initiator I_min mit der tiefsten Zerfallstemperatur eine Zerfallstemperatur T_min im Bereich von 60 bis 100°C hat,
• der Initiator I_max mit der höchsten Zerfallstemperatur eine Zerfallstemperatur T_max im Bereich von 100 bis 140°C hat, die Differenz von T_max und T_min größer als 10°C und I_max ein Perketal der allgemeinen Formel (1) ist,
  
  in der die Reste R¹ und R gleiche oder verschiedene Alkylreste mit 1 bis 5 Kohlenstoffatomen sind, wobei R¹ und R zu einem 5- oder 6-Ring verbunden sein können und R³ ein tert.-Butyl- oder tert.-Amylrest ist sowie
• weitere Initiatoren I_n, die gewünschtenfalls mitverwendet werden können, Zerfallstemperaturen T_n zwischen T_min und T_max aufweisen.

The present invention relates to bulk and suspension polymers

• a) 80 to 100 wt .-% methyl methacrylate and
• b) 0 to 20% by weight of further free-radically polymerizable monomers,

obtainable by polymerization at a temperature which is approximately constant over the majority of the polymerization time between 100 and 140 ° C. by means of an initiator system composed of at least two peroxidic initiators I of different decomposition temperatures T, at which half of the initiator has disintegrated after 1 h, whereby

• the initiator I _min with the lowest decay temperature has a decay temperature T _min in the range from 60 to 100 ° C.,
• the initiator I _max with the highest decay temperature has a decay temperature T _max in the range from 100 to 140 ° C., the difference between T _max and T _{min is} greater than 10 ° C. and I _{max is} a perketal of the general formula (1),
  
  in which the radicals R¹ and R are identical or different alkyl radicals having 1 to 5 carbon atoms, where R¹ and R can be linked to form a 5- or 6-ring and R³ is a tert-butyl or tert-amyl radical and
• further initiators I _n , which can be used if desired, have decomposition temperatures T _n between T _min and T _max .

In addition, the invention relates to a process for the preparation of these polymers and their use for the production of moldings and the moldings themselves.

The bulk and suspension polymerization of methyl methacrylate and optionally other monomers is generally known in numerous configurations. In the presence of radical polymerization initiators, for example organic peroxides and azo compounds, methyl methacrylate can be polymerize under an inert gas atmosphere usually at temperatures of 20 to 170 ° C under atmospheric or slightly elevated pressure. The molded parts made of these polymers, which are also referred to as "acrylic glass", are subject to high quality requirements, for example with regard to a low intrinsic color, high transparency, high surface gloss and freedom from bubbles and streaks. Since these properties depend, inter alia, on the residual monomer content, efforts are generally made to keep this residual monomer content as low as possible, for example by degassing the polymer or by choosing special polymerization conditions such as long polymerization times, specific temperature control or use of certain initiators.

According to the teaching of JP-B 71/03183, in the suspension polymerization of methyl methacrylate using an initiator system composed of lauroyl peroxide and 1,1-azobis-1-cyclohexanenitrile at 90 to 135 ° C., a residual monomer content of less than 0.3% by weight is achieved. ; however, at the expense of the relatively long polymerization time of 8 hours.

JP-A 87/177 001 recommends the use of two different initiators for the polymerization of monomers, including methyl methacrylate, 2,2-bis (t-butylperoxy) octane also being mentioned as the initiator.

From DE-A 2 756 035 it is known to polymerize vinyl monomers in at least two stages at a progressively higher temperature in the range from 70 to 150 ° C. by means of an initiator system from a more easily and a more difficult to decompose initiator, the more difficult to decompose a di tert-butyl perketal of an alkanoic acid ester. Among the large number of monomers that can be polymerized below, methyl methacrylate is also mentioned, but the experimental investigations deal only with styrene.

A similar process for the copolymerization of vinyl acetate with vinyl esters of other fatty acids is known from DE-A 2 229 569, the di-tert-butyl perketal of butanone being recommended as the initiator with a higher decomposition temperature.

The invention was based on high-quality substance and suspension polymers having a low residual monomer content and high light transmission based on methyl methacrylate, which are available in shorter polymerization times than before.

Accordingly, the polymers defined at the outset were found.

Furthermore, a process for their production has been found and their use for the production of moldings.

Homopolymers of methyl methacrylate are preferred. In addition, the polymers can also be composed of up to 20% by weight of further monomers, and preferably from
C₁-C₆ alkyl esters of acrylic acid,
C₂-C₆ alkyl esters of methacrylic acid and next to it
Acrylic and methacrylic acid,
Hydroxyalkyl esters,
Aminoalkyl esters and
Aminoalkylamides of acrylic and methacrylic acid with up to 6 carbon atoms in the alkyl radicals,
Acrylic and methacrylamide and their
N-alkyl and dialkyl derivatives with C₁-C₆ alkyl groups,
Vinyl esters of aliphatic C₂-C₁₈ carboxylic acids and
Vinyl aromatics such as styrene and α-methylstyrene
as well as mixtures of these monomers.

Suitable initiators I _min are, for example
aliphatic and aromatic diacyl peroxides such as
Diisononanoyl peroxide (T = 78 ° C),
Didecanoyl peroxide (T = 80 ° C),
Dilauroyl peroxide (T = 80 ° C),
Dibenzoyl peroxide (T = 91 ° C),
Peroxydicarbonate like
Diisopropyl peroxydicarbonate (T = 61 ° C) and
Alkyl peresters like
t-butyl perneodecanoate (T = 64 ° C),
t-amyl perpivalate (T = 71 ° C),
t-butyl perpivalate (T = 74 ° C) and
t-butyl per-2-ethylhexanoate (T = 92 ° C).

Initiators I _max are the percetals (1) according to the definition, among which
1,1-bis- (t-butylperoxy) -3,3,5-trimethylcyclohexane (T = 114 ° C),
1,1-bis (t-butylperoxy) cyclohexane (T 117 ° C) and
2,2-bis (t-butylperoxy) butane (T = 124 ° C) are preferred.

For a particularly uniform control of the polymerization and thus for the production of polymers with a molecular weight that is as uniform as possible, it is advisable to use further initiators I _n whose decomposition temperatures are between T _min and T _max , the decomposition temperatures of these initiators being different from one another or from T _min and T _max should differ by 10 to 20 ° C each.

Suitable initiators I _{n of this type} are those which have been specified for I _min and I _max . For the decomposition temperature range between 100 and 140 ° C you can, for example, dialkyl peroxides in addition to the perketals
t-butylcumyl peroxide (T 138 ° C) and
Alkyl peresters like
t-butyl perisononanoate (T = 119 ° C) and
t-butyl perbenzoate (T = 124 ° C)
use.

The values given for the decomposition temperatures T with a 1-hour half-life originate from company documents A 3.2.1 and A 3.7.1 "Organic Peroxides" from Peroxid-Chemie GmbH. Other possible initiators are given there.

The total amount of all initiators is preferably 0.001 to 1 mol%, particularly 0.01 to 0.1 mol%, based on the total amount of the monomers (a) and (b) used.

The proportion of initiators with the decomposition temperatures between 100 and 140 ° C. is preferably 20 to 80 mol%, in particular 30 to 60 mol%, based on the total amount of initiator, of which at least 25 mol% should be attributed to the perketal (1).

An improvement in the narrowest possible molecular weight distribution is achieved by the usual use of molecular weight regulators in amounts of 0.02 to 2% by weight, based on the total amount of monomers. Such regulators, with which an average molecular weight between 20,000 and 200,000 can be set depending on the amount, are preferably alkyl mercaptans such as n-dodecyl mercaptan and t-dodecyl mercaptan.

An essential feature of the invention is to carry out the polymerization over the majority of the polymerization time at an approximately constant temperature, that is to say in the narrowest possible temperature interval of ± 2 ° C. of an initial temperature once selected. Most of them are understood to mean at least 50% of the total time. A lower initial temperature and lower or higher temperatures towards the end of the polymerization, as well as deviations in the meantime, usually have no negative influence on the product quality, but isothermal reaction control over the entire polymerization time is fundamentally advantageous. If a temperature gradient - for example from the inside to the outside - can be observed in large-scale batches in the polymerization kettle, the temperature constancy applies to the temperature at the same point.

Since the polymerization temperature is above the boiling point of the methyl methacrylate, it is necessary to carry out the polymerization at least under the intrinsic pressure of the polymerization mixture, ie in the range from 1.1 to 2.5 bar. However, to avoid vapor bubbles it is particularly advantageous to work under a pressure which is 0.5 to 20 bar above the intrinsic pressure which the monomer mixture has at the chosen reaction temperature, this pressure being able to be generated by injecting an inert gas such as nitrogen .

Otherwise, the polymerization is carried out in a manner known per se according to the method of bulk polymerization or, preferably, suspension polymerization. To do this, the water and monomer phases are added with the addition of customary dispersants. For this purpose, water-soluble or water-solubilized substances such as pectins, gelatin, methyl cellulose or other cellulose ethers are suitable. Polyvinyl alcohol, alkali metal salts of polyacrylic acid or polymethacrylic acid or alkali metal salts of copolymers of methyl methacrylate and methacrylic acid can also be used. In addition, the water phase can be buffered; Salts of phosphoric acid, for example mixtures of potassium dihydrogen phosphate and disodium hydrogen phosphate, are customary for the alkaline range.

To improve the processing properties, thermal stabilizers, e.g. hindered phenols and lubricants, e.g. Stearic acid can be added.

The molecular weight regulator and the initiator system according to the invention are in the monomer phase.

The reaction mixture is rendered inert by repeated injection of an inert gas such as nitrogen and subsequent expansion. After the inert gas has been injected again, the monomer phase is first dispersed in the cold by stirring in the water phase and then heated to the polymerization temperature which is above the boiling point of methyl methacrylate in the range from 100 to 140.degree. The pressure in the boiler is between 2 and 100 bar. The polymerization is generally complete after a reaction time of 4 hours.

The polymers according to the invention are distinguished by a low intrinsic color, high transparency, high surface gloss and freedom from bubbles and streaks, have a residual monomer content of usually less than 0.4% by weight and are in the particularly short polymerization times of about 2 to 4 hours available.

Examples 1 to 5

Eine Mischung aus 190 kg

vollentsalztem Wasser,

1,4 kg

des Natriumsalzes eines Copolymerisates aus 64 Gew.-% Methacrylsäure und 36 Gew.-% Methylmethacrylat in Form einer 1,6 gew.-%igen wäßrigen Lösung als Dispergiermittel und

1,4 kg

Natriumphosphathydrat als Puffer sowie

der aus der Tabelle ersichtlichen Monomerphase, welche die ebenfalls dort angegebenen Mengen verschiedener Initiatorsysteme sowie den Regler n-Dodecylmerkaptan enthielt, wurde bei Raumtemperatur zunächst mehrmals mit Stickstoff gespült, sodann 0,5 bar Stickstoff aufgepreßt, anschließend unter Rühren auf 125°C erhitzt und 3 h bei dieser Temperatur gehalten. Nach Abkühlung und Entspannung wurde das Polymerisat abgetrennt, gewaschen und getrocknet.

A mixture of 190 kg

demineralized water,

1.4 kg

the sodium salt of a copolymer of 64 wt .-% methacrylic acid and 36 wt .-% methyl methacrylate in the form of a 1.6 wt .-% aqueous solution as a dispersant and

1.4 kg

Sodium phosphate hydrate as a buffer as well

The monomer phase shown in the table, which also contained the amounts of various initiator systems and the regulator n-dodecyl mercaptan, was first flushed with nitrogen several times at room temperature, then pressurized with 0.5 bar of nitrogen, then heated to 125 ° C. with stirring and 3 h held at this temperature. After cooling and relaxation, the polymer was separated off, washed and dried.

Examples 6 and 7

4000 kg of water phase, consisting of demineralized water, dispersant and buffer according to Examples 1 to 5, were at room temperature together with the monomer phase shown in the table, which contained the amounts of various initiator systems, the regulator n-dodecyl mercaptan and the lubricant stearic acid flushed several times with nitrogen while stirring. After pressing an N₂ pressure of 0.5 bar, the mixture was heated to 128 ° C and held at this temperature for 3 hours, the pressure in the boiler being about 4 bar. The reaction mixture was worked up according to Examples 1 to 5.

• Restmonomerengehalt
• Schmelzindex (MFI, 230°C/3,8 kp) nach DIN 53 735
• Lösungsviskosität nach DIN 51 562
• UV-Transmission.

The following properties were measured for quality control:

• Residual monomer content
• Melt index (MFI, 230 ° C / 3.8 kp) according to DIN 53 735
• Solution viscosity according to DIN 51 562
• UV transmission.

The residual monomer content was measured using gas chromatographic headspace analysis, a method for determining evaporable components in liquids and solids (including monomers in thermoplastics).

The melt index MFI (dimension g / 10 min), also called melt flow index, is an internationally used, depending on the degree of polymerization, characteristic value for the flow behavior of thermoplastics. It indicates the amount of a polymer which is squeezed out of a cylindrical cavity in 10 min through a standardized nozzle by means of a stamp of certain specific load. The melt index decreases sharply with increasing degree of polymerization; the smaller its value, the more difficult to flow, i.e. The polymer is of higher molecular weight.

$$\frac{\text{η}}{{\text{η}}_{\text{o}}}\text{= Viskositätsverhältnis}$$

mit

η =

Viskosität der Polymerlösung definierter Konzentration

η_o =

Viskosität des Lösungsmittels

C = Konzentration der Lösung in g/ml.The solution viscosity is given by the viscosity number VZ, which indicates the relative increase in the viscosity of a solvent by 0.1 to 1.0 g / 100 ml of dissolved polymer divided by the concentration in g / 100 ml. The viscosity numbers increase with the degree of polymerization.

$$\frac{\text{η}}{{\text{η}}_{\text{O}}}\text{= Viscosity ratio}$$

With

η =

Viscosity of the polymer solution of a defined concentration

η _o =

Viscosity of the solvent

C = concentration of the solution in g / ml.

The measurement of the UV transmission is used to check the UV light transmittance of the polymer, which can be impaired by residual amounts of initiators. Since high UV transmission is required for polymethyl methacrylate, a transmission of at least 65% at 300 nm is necessary.

The details of these tests and their results can be found in the table.

• 1) Dilauroylperoxid
• 2) t-Butyl-per-2-ethylhexanoat
• 3) t-Butyl-per-3,5,5-trimethylhexanoat
• 4) 2,2-Bis-(t-butylperoxy)-butan; 50 %ige Lösung in Aliphaten (genauere Angaben zur Zusammensetzung sind nicht möglich, da es ein Handelsprodukt der Firma Peroxid Chemie GmbH ist)
• 5) 2,2-Bis-(t-butylperoxy)-butan; 50 %ige Lösung in Weißöl
• 6) 1,1-Bis-(t-butylperoxy)-cyclohexan; 50 %ige Lösung in Weißöl

Explanations to the table:

• 1) Dilauroyl peroxide
• 2) t-Butyl-per-2-ethylhexanoate
• 3) t-Butyl-per-3,5,5-trimethylhexanoate
• 4) 2,2-bis (t-butylperoxy) butane; 50% solution in aliphatic (more detailed information on the composition is not possible since it is a commercial product from Peroxid Chemie GmbH)
• 5) 2,2-bis (t-butylperoxy) butane; 50% solution in white oil
• 6) 1,1-bis (t-butylperoxy) cyclohexane; 50% solution in white oil

Claims (11)

1. A mass or suspension polymer of

   a) from 80 to 100% by weight of methyl methacrylate and

   b) from 0 to 20% by weight of further monomers capable of undergoing free radical polymerization,

   obtainable by polymerization at a temperature of from 100 to 140°C, virtually constant over the major part of the polymerization time, by means of an initiator system of two or more peroxide initiators I having different decomposition temperatures T at which half of each initiator has decomposed after 1 hour, wherein

   - the initiator I_min having the lowest decomposition temperature has a decomposition temperature T_min of from 60 to 100°C,

   - the initiator I_max having the highest decomposition temperature has a decomposition temperature T_max of from 100 to 140°C, the difference between T_max and T_min is greater than 10°C and I_max is a perketal of the general formula (1)

   

   where R¹ and R are identical or different alkyl radicals of 1 to 5 carbon atoms and may be bonded to form a 5-membered or 6-membered ring and R³ is tert-butyl or tert-amyl, the amount of initiator I_max being from 20 to 80 mol %, based on the total amount of catalyst, and

   - further initiators I_n which, if desired, may be concomitantly used have decomposition temperatures T_n of from T_min to T_max, with the proviso that the polymerization time is no longer than four hours.
2. A mass or suspension polymer as claimed in claim 1, obtainable from acrylic acid; methacrylic acid, C₁-C₆-alkyl esters of acrylic acid and/or C₂-C₆-alkyl esters of methacrylic acid as comonomer (b).
3. A mass or suspension polymer as claimed in claim 1 or 2, obtainable by using
      1,1-bis-(tert-butylperoxy)-3,3,5-trimethylcyclohexane,
      1,1-bis-(tert-butylperoxy)-cyclohexane or
      2,2-bis-(tert-butylperoxy)-butane as initiator I_max.
4. A mass or suspension polymer as claimed in any of claims 1 to 3, obtainable using a total of from 0.01 to 0.1 mol %, based on the total amount of the monomers, as the total amount of all initiators.
5. A mass or suspension polymer as claimed in any of claims 1 to 4, obtainable using from 25 to 100 mol %, based on the initiators, of perketals (1) whose decomposition temperature is from 100 to 140°C.
6. A mass or suspension polymer as claimed in any of claims 1 to 5, obtainable with the concomitant use of an alkyl mercaptan as a molecular weight regulator.
7. A process for the preparation of a mass or suspension polymer of

   a) from 80 to 100% by weight of methyl methacrylate and

   b) from 0 to 20% by weight of further monomers capableof undergoing free radical polymerization,

   by polymerization by means of an initiator system consisting of two or more initiators I having different decomposition temperatures T of from 60 to 140°C, at which in each case half the initiator has decomposed after 1 hour, wherein

   - the initiator I_min having the lowest decomposition temperature possesses a decomposition temperature T_min of from 60 to 100°C,

   - the initiator I_max having the highest decomposition temperature possesses a decomposition temperature T_max of from 100 to 140°C, the difference between T_max and T_min is greater than 10°C and I_max is a perketal of the formula (1)

   

   where R¹ and R are identical or different alkyl radicals of 1 to 5 carbon atoms and R¹ and R may be bonded to form a 5-membered or 6-membered ring and R³ is tert-butyl or tert-amyl, and

   - further initiators I_n which, if desired, may be concomitantly used have a decomposition temperature T_n of from T_min to T_max and

   - the polymerization temperature is from 100 to 140°C and is kept virtually constant over the major part of the polymerization time, which is no longer than four hours.
8. A process for the preparation of a mass or suspension polymer as claimed in claim 7, wherein the polymerization is carried out by forcing in an inert gas under a pressure which is from 0.5 to 20 bar above the autogenous pressure of the monomer mixture at the chosen reaction temperature.
9. The use of a mass suspension polymer as claimed in claim 1 for the production of moldings.
10. A molding obtained from a polymer as claimed in claim 1.
11. The use of an initiator system consisting of two or more peroxide initiators I having different decomposition temperatures T at which half of each initiator has decomposed after 1 hour, wherein

    - the initiator I_min having the lowest decomposition temperature has a decomposition temperature T_min of from 60 to 100°C,

    - the initiator I_max having the highest decomposition temperature has a decomposition temperature T_max of from 100 to 140°C, the difference between T_max and T_min is greater than 10°C and I_max is a perketal of the general formula (1)

    

    where R¹ and R are identical or different alkyl radicals of 1 to 5 carbon atoms and may be bonded to form a 5-membered or 6-membered ring and R³ is tert-butyl or tert-amyl, and

    - further initiators I_n which, if desired, may be concomitantly used have decomposition temperatures T_n of from T_min to T_max, for the preparation of a mass or suspension polymer of

    a) from 80 to 100% by weight of methyl methacrylate and

    b) from 0 to 20% by weight of further monomers capableof undergoing free radical polymerization

    by polymerization at a temperature of from 100 to 140°C which is virtually constant over the major part of the polymerization time.